Tänk om- : seriösa vetenskapliga svar på absurda hypotetiska frågor

What If?: Serious Scientific Answers to Absurd Hypothetical Questions is a non-fiction book by Randall Munroe in which the author answers hypothetical science questions sent to him by readers of his webcomic, xkcd. The book contains a selection of questions and answers originally published on his blog What If?, along with several new ones. The book is divided into several dozen chapters, most of which are devoted to answering a unique question. What If? was released on September 2, 2014 and was received positively by critics.